Abstract Access control equipment comprises an interrogation unit (IU) having means (14) for emitting an interrogation signal, and a plurality of transponders (e.g. T), each transponder (T) having a stored identity code different from that of the other transponders (T). This identity code comprises a plurality of fields each holding a selected information bit. The interrogation signal is controlled so as simultaneously to interrogate the fields of all transponders (T) within range in a serial manner. A group reply signal is sent back to the interrogation unit (IU) from any transponder (T) having, in the field being interrogated, a bit matching that required by the interrogation signal. The interrogation unit (IU) is arranged to determine, from the series of received reply signals, the identity of each and every valid transponder (T) within range.
Access control equipment comprising an interrogation unit having means for emitting an interrogation signal, and a plurality of transponders having means for receiving the interrogation signal, each transponder having a stored identity code different from that of the other transponders, the identity code comprising a plurality of fields each holding an information bit selected from a plurality of possible bits, means for controlling the interrogation signal so that it simultaneously interrogates the fields of all transponders within range in a serial manner, means for sending a group reply signal to the interrogation unit from any transponder having in the field been interrogated a bit matching that required by the interrogation signal, and means in the interrogation unit for converting the series of group reply signals to the encrypted identification codes of those transponders within range.
Claim 2
Dependent Claim
135 words
Access control equipment comprising an interrogation unit having means for emitting an interrogation signal, and a plurality of transponders having means for receiving the interrogation signal, each transponder having a stored identity code different from that of the other transponders, the identity code comprising a plurality of fields each holding an information bit selected from a plurality of possible bits, means for controlling the interrogation signal so that it simultaneously interrogates the fields of all transponders within range in a serial manner, means for sending a group reply signal to the interrogation unit from any transponder having in the field been interrogated a bit matching that required by the interrogation signal, and means in the interrogation unit for converting the series of group reply signals to the encrypted identification codes of those transponders within range.
Claim 3
Dependent Claim
41 words
Access control equipment as claimed in claim 1, in which the transponder reply signals differ on and during successive searches and are encrypted according to a different control code transmitted by the interrogation unit at the beginning of each interrogation cycle.
Claim 4
Dependent Claim
56 words
Access control equipment as claimed in claim 2, in which a valid transponder within range of the interrogation unit replies to its final interrogation step with an encoded signal generated from the control code transmitted at the beginning of the interrogation cycle and from a further identification code and an algorithm both held by the transponder.
References Cited (Backward Citations)
No citation records indexed.
USPTO Annuity & Maintenance Windows
Maintenance schedule is calculated for granted US utility patents.